In magnetic storage devices such as, for example, a hard disk, the data is stored on an active surface covered with a ferromagnetic material and divided into a plurality of cells. Each cell stores one bit of data represented by a change in the magnetization state of the ferromagnetic material.
Data is read from and written on the disk by means of a head, typically an electromagnetic head. In particular, the electromagnetic head comprises a magnetic core interrupted by an air-gap disposed close to the active surface of the disk. The core defines a magnetic circuit for a flux generated by a coil wound around the magnetic core. During a writing operation, a certain current flows in the coil and the corresponding magnetic flux is linked with an underlying memory cell so as to vary its magnetization state.
The electromagnetic head also comprises a magnetoresistive element such as, for example, a transverse magnetoresistor, the resistance of which varies as a function of an external magnetic field. During a reading operation, the change in magnetic flux generated by the underlying memory cell is linked partially by the magnetoresistor. The magnetization state of the underlying cell can thus be determined by measurement of the resistance of the magnetoresistor.
The magnetoresistor is generally disposed beneath the air-gap of the magnetic core as described, for example, in WO 96/08814. In a different known structure, described in U.S. Pat. No. 4,901,177, the magnetic core is interrupted by two further air-gaps, adjacent each of which a magnetoresistor is disposed. In known electromagnetic heads, the magnetoresistor is in any case electrically insulated from the magnetic core.
A disadvantage of these known solutions is that the electromagnetic head has low sensitivity since the change in magnetic flux generated by the memory cell is not completely linked by the magnetoresistor.